Bluetooth Windows: fix segfault in COM de-init

While doing COM initialization/deinitialization, we always implicitly
assumed that QCoreApplication instance is available.
However, if the Bluetooth objects are re-parented to the main
application, the QCoreApplication instance will already be removed by
the time we want to delete the Bluetooth object (and call COM de-init).

Fix it by caching the main application's thread, and using it instead
of QCoreApplication::instance()->thread() in the mainThreadCoUninit()
helper method.

This commit still assumes that all Bluetooth objects are created
*after* the main QCoreApplication instance.

Amends 340b84a5578f78d7a399e369e900ac991d9e0da2.

Fixes: QTBUG-119063
Pick-to: 6.7 6.6 6.5 6.2
Change-Id: I450e4e14039ca27fcfd1f3f131789b049e1edb03
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

1 files changed, 11 insertions, 4 deletions

diff --git a/src/bluetooth/qbluetoothutils_winrt.cpp b/src/bluetooth/qbluetoothutils_winrt.cpp
index ca4326f8..b146be19 100644
--- a/src/bluetooth/qbluetoothutils_winrt.cpp
+++ b/src/bluetooth/qbluetoothutils_winrt.cpp
@@ -43,6 +43,7 @@ QByteArray byteArrayFromBuffer(const ComPtr<NativeBuffer> &buffer, bool isWCharS
 }
 
 static QSet<void*> successfulInits;
+static QThread *mainThread = nullptr;
 
 void mainThreadCoInit(void* caller)
 {
@@ -58,27 +59,33 @@ void mainThreadCoInit(void* caller)
         return;
     }
 
+    Q_ASSERT_X(!mainThread || mainThread == QThread::currentThread(),
+               __FUNCTION__, "QCoreApplication's thread has changed!");
+
     // This executes in main thread which may run Gui => use apartment threaded
     if (!SUCCEEDED(CoInitializeEx(NULL, COINIT_APARTMENTTHREADED))) {
         qCWarning(QT_BT_WINDOWS) << "Unexpected COM initialization result";
         return;
     }
     successfulInits.insert(caller);
+    if (!mainThread)
+        mainThread = QThread::currentThread();
 }
 
 void mainThreadCoUninit(void* caller)
 {
     Q_ASSERT(caller);
 
-    if (QThread::currentThread() != QCoreApplication::instance()->thread()) {
-        qCWarning(QT_BT_WINDOWS) << "Main thread COM uninit tried from another thread";
+    if (!successfulInits.contains(caller)) {
+        qCWarning(QT_BT_WINDOWS) << "COM uninitialization without initialization";
         return;
     }
 
-    if (!successfulInits.contains(caller)) {
-        qCWarning(QT_BT_WINDOWS) << "COM uninitialization without initialization";
+    if (QThread::currentThread() != mainThread) {
+        qCWarning(QT_BT_WINDOWS) << "Main thread COM uninit tried from another thread";
         return;
     }
+
     CoUninitialize();
     successfulInits.remove(caller);